Child support is based on the policy that parents are obligated to pay for the support of their children, even when the children are not living with both biological parents. Though courts typically permit visitation rights to non-custodial parents, in such separations one parent is often awarded custody and the role of primary caregiver. In such cases, the other parent still remains obligated to pay a proportion of the costs involved in raising the child. Child support may also be ordered to be paid by one parent to another when both parents are custodial parents and they share the child raising responsibilities. In rare cases, a parent with sole custody of his or her children may be ordered to pay child support to the noncustodial parent to support the children while they are in the care of that parent.

These costs are still legally obligatory, even when the paying parent has been legally limited or prevented by the other parent from participating in or making decisions involving the upbringing of the child or children. It is also important to note the custodial parent is expected to pay a percentage of the costs incurred raising a child, even if a non-custodial parent has been ordered to make child support payments. In Massachusetts, for example, it is the responsibility of the custodial parent alone to pay the first $100 in all uninsured medical costs for each child, per year. Only then will the courts consider authorizing child-support money from a non-custodial parent to be used for said costs.

In most jurisdictions there is no need for the parents to be married, and only paternity and/or maternity (filiation) need to be demonstrated for a child support obligation to be found by a competent court. Child support may also operate through the principle of estoppel where a de facto parent that is in loco parentis for a sufficient time to establish a permanent parental relationship with the child or children. In many states the principle of estoppel can be used to require a person to pay child support even if the assumption of a parental relationship was the result of a fraudulent misrepresentation of paternity by the mother.